A woman has her face doused with milk after being exposed to tear gas on the streets of Ferguson, Mo.

Photo: Joshua Lott, Getty Images

A woman has her face doused with milk after being exposed to tear...

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The Rev. Audrey Hollis prays during a sermon in Ferguson, Mo., where Michael Brown was killed.

Photo: Joe Raedle, Getty Images

The Rev. Audrey Hollis prays during a sermon in Ferguson, Mo.,...

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FERGUSON, MO - AUGUST 17: A demonstrator stands near a cloud of tear gas after police fired the gas at demonstrators protesting the shooting death of Michael Brown when they remained on the street after a midnight curfew on August 17, 2014 in Ferguson, Missouri. Police fired smoke bombs and tear gas at protesters who remained on the streets of Ferguson after a Saturday night curfew took effect. Violent outbreaks have taken place in Ferguson since the shooting death of Michael Brown by a Ferguson police officer on August 9th. (Photo by Joe Raedle/Getty Images)

Photo: Joe Raedle, Getty Images

FERGUSON, MO - AUGUST 17: A demonstrator stands near a cloud of...

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FERGUSON, MO - AUGUST 17: A demonstrator throws a tear gas canister back at police after they fired the gas at them while protesting the shooting death of Michael Brown on August 17, 2014 in Ferguson, Missouri. Police sprayed pepper spray, shot smoke, gas and flash grenades as violent outbreaks have taken place in Ferguson since the shooting death of Michael Brown by a Ferguson police officer on August 9th. (Photo by Joe Raedle/Getty Images)

Photo: Joe Raedle, Getty Images

FERGUSON, MO - AUGUST 17: A demonstrator throws a tear gas...

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Police wait to advance after tear gas was used to disperse a crowd Sunday, Aug. 17, 2014, druing a protest for Michael Brown, who was killed by a police officer last Saturday in Ferguson, Mo. As night fell Sunday in Ferguson, another peaceful protest quickly deteriorated after marchers pushed toward one end of a street. Police attempted to push them back by firing tear gas and shouting over a bullhorn that the protest was no longer peaceful. (AP Photo/Charlie Riedel)

Ferguson, Mo. -- Police used tear gas to clear protesters off the streets late Sunday, a week after demonstrations against the fatal police shooting of a black Missouri teenager filled this St. Louis suburb with angry, defiant crowds.

As night fell in Ferguson, the protest quickly deteriorated after marchers pushed toward one end of a street. Police pushed them back by repeatedly firing tear gas.

The latest confrontation unfolded hours after Attorney General Eric Holder ordered a federal medical examiner to perform another autopsy on 18-year-old Michael Brown, who was fatally shot by a white police officer.

The "extraordinary circumstances" surrounding his death and a request by Brown's family members prompted the Justice Department's decision to conduct an autopsy, agency spokesman Brian Fallon said in a statement.

Federal officials are reviewing the Aug. 9 shooting of Brown, who was unarmed, to determine if there were any civil rights violations, while local officials said they are trying to determine whether the officer was justified in using lethal force.

The latest clashes erupted three hours before a midnight curfew imposed by Gov. Jay Nixon. Officers in riot gear ordered all the protesters to disperse. Many of the marchers retreated, but a group of about 100 stood defiantly about two blocks away until getting hit by a volley of tear gas.

The protests have been going on since Brown's death heightened racial tensions between the predominantly black community and the mostly white Ferguson Police Department, leading to several run-ins between police and protesters.

At a Sunday rally, the Rev. Al Sharpton said Brown's death was a "defining moment for this country." Sharpton wants Congress to stop programs that provide military-style weaponry to police departments. He also condemned the violence and looting in Ferguson.

Police have said little about the encounter between Brown and the officer - identified as Darren Wilson - except to say that it involved a scuffle in which the officer was injured and Brown was shot. Witnesses say the teenager had his hands in the air as the officer fired multiple rounds.

Autopsy findings

Michael Brown was shot at least six times, including twice in the head, a preliminary private autopsy performed Sunday found.

One of the bullets entered the top of Brown's skull, suggesting his head was bent forward when it struck him and caused a fatal injury, according to Dr. Michael Baden, the former chief medical examiner for New York City, who flew to Missouri on Sunday at the family's request to conduct the separate autopsy.

Brown, 18, was also shot four times in the right arm, he said.

Attorney General Eric Holder said the Justice Department would conduct its own autopsy, in addition to the one performed by local officials and this private one.

The preliminary autopsy results are the first time that some of the critical information resulting in Brown's death has been made public.

"People have been asking: How many times was he shot? This information could have been released on day one," Baden said.